Research On Street Spatial Outline Based On Viewshed Analysis

Street space is an important part of urban public space and the form of the street space outline affects the street space pattern to a large extend. From the perspective of visual perception of the street space, this paper aims to research the method of defining street spatial outline based on viewshed analysis in GIS.In An approach for simulating the street spatial patterns, Ding W. and Tong Z. achieved to measure the variance between the form of the urban fabric and the street viewshed pattern based on the viewshed analysis in GIS. However, the definition of street space outline is a key step to visual data extraction and further analysis. Ding W. and Tong Z. simplified this problem empirically without convincing arguments. Based on Ding and Tong’s studies, this paper aims to do research into the method to define the street spatial outline and examine whether the conclusions in (Ding W. and Tong Z.,2011) is still correct.In the downtown of some large cities in China, the buildings along the street are often disordered, and it is hard to find morphological connection between the building pattern and street pattern. Because of the gaps between buildings along the street, the boundary of the street space is often vague. And then how to define the visual boundary of the gaps in streets is a key point to the street spatial outline definition.This paper focuses on the gap space between buildings along the street. By studying the form of the gap, three street ideal models with all kinds of gaps are organized. Bringing in the factor of speed, this paper compares the visual data on the different T-n outlines of the street ideal models and find T-9 outline can characterize the street space in 3 kinds of speed precisely with minimum error. And then the method of defining the street spatial outline is achieved.Based on the street spatial outline, this paper re-analyses the six street samples in (Ding W. and Tong Z.,2011) and the method of street spatial outline definition proposed in this paper is proved to be reasonable.